Gas lasers offer limited power output capabilities per unit length. The upper limit for a sealed, waveguide Co.sub.2 laser is about 0.6 watts/cm: therefore, a 30 watt CO.sub.2 laser has a resonator length of about 50 cm. The resulting system architectures are mechanically complex, are not rugged or reliable, and have restricted portability. When waveguide lasers are used with a ceramic bore material, long resonator lengths imply considerable manufacturing difficulties because of tight machine tolerances, poor yields, and high production costs.
Chenausky et al, in U.S. Pat. Nos. 4,429,398 and 4,438,514, addresses the length problem by using mirrors to fold the optical path, achieving some reduction in overall resonator length at the expense of a modest increase in width. In the '398 patent two parallel waveguides are optically coupled by a pair of folding mirrors within a common block. This configuration results in a finite amount of diffraction losses that can be reduced but not eliminated by minimizing the distance traveled in free space. The '514 patent shows a progressive improvement which uses a third diagonal waveguide that connects, end-to-opposite-end, the two parallel waveguides. Since the waveguides are serially connected, the laser cavity will have a series of parallel waveguides, or a Z-folded waveguide arrangement.
De Maria, in U.S. Pat. No. 3,361,987, increases active gain length in a polysided folded laser path in resonators employing solid or liquid amplifier media, with a continuous folded optical path, using total internal reflection. Nakagome et al in U.K. Application No. 2,033,648A employs a similar configuration for achieving long optical paths in semiconductor light amplifiers. The use of total internal reflection by De Maria and Nakagome requires that the refractive indices of the laser medium and the matching medium be selected to achieve the proper angle of reflection. The matching medium may surround the laser medium, or may be deposited on the end faces of the solid medium. De Maria suggest the use of a ruby laser element immersed in liquid oxygen. The required index matching significantly increases the difficulty of manufacturing and operating the laser. In gas lasers with the index of refraction differing from unity by a few parts per million, total internal reflection cannot be used as an optical path folding technique.
Patent Application No. 052,977 U.S. Pat. No. 4,815,094, entitled `MULTIPLY FOLDED LASER SYSTEMS` by Armando Cantoni, was filed in the U.S. Patent Office on May 22, 1987. This invention discloses a laser resonator having multiply folded optical paths in a region by employing a series of front surface reflecting elements. In these novel and unique configurations, a dramatic reduction in the size of the laser resonators is achieved by multiply folding the optical paths. The Cantoni application is incorporated herein by reference.
Successful implementation of laser-based systems can greatly benefit from a more compact design of the laser resonator. In particular, the length of the optical laser cavity appears to be the limiting parameter. Virtually all applications that require protability and ruggedness are enhanced by a reduction in overall resonator size.